单组分双分析通道红外气体检测方法研究

基于单分析通道非分散红外(non-dispersive infrared, NDIR)气体分析技术, 提出一种单组分双分析通道气体检测方法. 根据SO₂的红外吸收特征, 采用逐线积分气体吸收模型和方法, 选择洛伦兹展宽线型并考虑温度和气压对积分线强、线型的影响, 确定了两个分析通道的滤波参数.使用7.32 μm和4 μm波段分别反演小于等于 280 ppm与大于280 ppm的SO₂浓度;使用最小二乘法, 以三阶多项式为拟合模型, 获得了两个分析通道的定标曲线.对系统的测量线性度、检测限和测量准确度进行了分析. 两个分析通道的联合可以实现约几ppm至10000 ppm的宽动态范围的SO₂测量, 且系统测量线性度大于0.99, 测量误差小于5%.既克服了NDIR气体分析技术检测灵敏度和宽动态测量范围不能同时兼顾的缺陷, 良好的系统测量线性度还为多组分气体分析的干扰修正提供了非常必要的前提条件.     

逐线积分气体吸收模型及其在NDIR气体检测中的应用

介绍了一种精确的逐线积分痕量气体吸收模型,模型适用于中红外波段大气环境中痕量气体、污染气体检测的理论研究和工程应用。首先介绍了气体辐射特性的理论计算方法和现有逐线积分大气模 型,比较了各自的优劣性,其次详述了逐线积分计算的理论: 吸收系数是温度、波长、气体浓度和相关吸收线参数的函数,单条谱线的平均吸收系数是积分线强与谱线线型的卷积,在不同的大气条件下选 择不同的线型。最后,详细描述了模型的算法细节,并给出了模型计算的结果与傅里叶变换光谱仪实测数据的对比,举例介绍了吸收模型在NDIR气体探测技术中的实际应用,并使用该模型模拟了NDIR探 测器两个通道的信号强度随尾气中CO₂,CO浓度变化的关系,通过计算确定了NDIR探测器合适的工作范围。所述模型利用HITRAN光谱数据库,考虑了展宽、线翼截断、温度修正、光谱分辨 率变化等情况,可以有效的模拟大气环境中多种气体的红外吸收特征。     

CO和CO2的1.58μm波段可调谐二极管激光吸收光谱的二次谐波检测研究

红外可调谐二极管激光吸收光谱技术作为新的痕量气体监测分析方法,在大气化学研究和污染气体监测中得到了应用.文章介绍利用可调谐二极管激光吸收光谱学(TDLAS)技术对常压下的CO和CO2的近红外波段光谱静态测量研究和洛伦兹线型下的CO2二次谐波光谱与调制度的关系.     

非线性吸收对多组分气体分析的影响及其修正方法

利用非分散红外(NDIR)技术研究了非线性吸收现象对多组分气体分析交叉干扰扣除的影响及其修正方法。理论上推导了由于非线性吸收导致的干扰系数变化对系统测量准确度的影响。对常规的干扰方程组进行了修正,使用干扰函数来定量分析气体间的交叉干扰,当测量气体存在非线性吸收时,干扰函数也会发生相应变化。基于最小二乘法,以三阶多项式为拟合模型,拟合出了系统的干扰函数。利用拟合的干扰函数,通过实验证明了提出的修正方法在系统存在非线性吸收现象时仍能有效地扣除气体间的交叉干扰。     

基于反转法的CO2-O2混合物导热系数预测

采用反转法获得了CO2-O2的新势能,通过迭代计算提高了势能精度,在此基础上,给出了新势能的碰撞积分和特征参数.利用新的势能参数,根据分子动力学理论与WCUB理论,预测了CO2-O2混合气体零密度时的导热系数,计算的温度范围为273.15～3273.15 K,结果与实验数据的绝对平均偏差和最大偏差分别为3.87%和4....     

适应积分时间调整的红外图像非均匀性校正方法

针对应用常规红外图像非均匀性校正方法在变积分时间时,图像灰度值会发生改变的现象,提出了一种适应积分时间调整的红外图像非均匀性校正方法.该方法将不同积分时间、不同温度的黑体定标数据和对应的理论红外辐射量整合为一个整体数据库,借助神经网络损失函数和误差反向传递机制,对模型中的校正系数进行学习.训练得到的校正网络能在红外相机积分时间实时调整过程中,保证图像均匀地稳定输出,对后端红外图像处理有着重要意义,并验证训练该网络不需要大量定标数据.而针对红外探测器响应漂移的现象,则提出了在线修正校正系数的方法以有效应对.     

光声光谱多组分气体分析仪的交叉干扰特性研究

设计了一套基于红外热辐射光源的光声光谱多组分气体分析仪。通过分析多组分气体间交叉干扰的主要因素以及特征气体的红外吸收谱线,确定了中红外带通滤光片的参数。利用标准气体对设计的光声光谱仪进行标定,研究了待测气体之间交叉干扰的定量关系,并利用湿度发生器对装置受到水气干扰情况进行分析。实验结果表明,C₂H₂对CH₄、CH₄对C₂H_6的干扰水平分别达到10.49μV/(μL/L)、18.66μV/(μL/L),其他烃类气体间的干扰可以忽略。CO₂对CO、CH₄、C₂H₂和C₂H₄干扰响应度分别为1.615μV/(μL/L)、0.055μV/(μL/L)、0.130μV/(μL/L)以及0.016μV/(μL/L)。此外,水气对C₂H₂、CH₄、C₂H_6、C₂H₄、CO和CO₂都会产生一定的干扰,干扰的响应度分别为0.591μV/(μL/L)、0.421μV/(μL/L)、0.071μV/(μL/L)、0.007μV/(μL/L)、0.051μV/(μL/L)和0.055μV/(μL/L)。实验结果表明C₂H₂对CH₄、CH₄对C₂H_6、CO₂对CO以及高浓度水气对其他气体的检测会产生较高水平的干扰,在测量过程中应当考虑扣除。     

激光外差光谱仪的仪器线型函数研究

激光外差是一种基于相干探测原理的高灵敏度光谱检测技术,因其同时具有很高的光谱分辨能力,被广泛应用于诸多研究领域.在光谱测量过程中,仪器线型函数对吸收谱线的平滑作用,会对气体浓度的反演结果产生影响.为了获取激光外差光谱仪的仪器线型函数,基于激光外差原理和信号处理过程,对影响仪器线型函数的射频滤波带宽和积分时间等参数进行了分析,获得了仪器线型函数表达式.利用自行建立的激光外差光谱仪,多次测量了3.53μm波段内水汽、甲烷的吸收谱线,分别将射频滤波频域响应函数和本文获得的仪器线型函数耦合进水汽、甲烷柱浓度的反演.结果表明,射频滤波带宽为30 MHz、积分时间分别为10 ms和100 ms时,光谱仪的实际分辨率分别约为0.005 cm~(-1)和0.025 cm~(-1);使用仪器线型函数对积分时间为100 ms时测量的数据进行反演,透过率残差平方和与甲烷吸收峰值处的残差分别减小16%和100%,提高了气体浓度反演的准确度.     

混合气体测量中重叠吸收谱线交叉干扰的分离解析方法

在基于可调谐二极管激光吸收光谱技术(tunable diode laser absorption spectroscopy,TDLAS)进行多种组分混合气体测量时,经常会遇到吸收谱线之间存在相互干扰的现象,这也是使用该技术测量过程中的主要"瓶颈".比如在前期的应用中:微量一氧化碳(CO)和甲烷气体(CH_4)在同时检测时两者的吸收谱线存在严重的重叠干扰现象,特别是在高浓度CH_4存在的环境下,微量CO气体吸收信号会被干扰甚至湮没,无法实现有效解调,这是通过谱线选取所不能解决的问题.因此,针对此问题本文提出了基于支持向量回归模型,以CO和CH_4吸收谱线的严重重叠干扰问题为例,通过选择线性核函数建立CO支持向量回归模型和CH_4支持向量回归模型,可对CO和CH_4的混合气体吸收谱线进行解调,最终获得两种气体浓度的准确测量结果.通过实验分别实现了四种不同浓度CH_4环境下微量CO气体的检测,得到的CO和CH_4浓度(气体的体积分数)测量的绝对误差分别小于2 × 10~(-6)和0.2 × 10~(-2);通过不同浓度的固定配比实验分析,CO和CH_4气体的测量值与实际值之间的相关系数分别达到了 0.998和0.9995,且CO和CH_4气体测量结果的绝对误差分别不超过2 × 10~(-6)和0.1 × 10~(-2),完全满足了混合气体的精确测量,为实现多场合混合气体目标的实时监测提出了解决方案.     

一种单光谱吸收积分吸光度快速计算方法及应用

可调谐半导体激光吸收光谱技术(TDLAS)作为一种痕量气体精确检测的方法,已广泛应用于生活生产之中,该方法可通过积分吸光度与气体浓度的线性关系准确反演待测气体的浓度。环境变化和系统噪声等易造成吸光度曲线发生变形,故需对吸光度曲线进行非线性拟合,将其回归至Voigt模型。设计并搭建了基于TDLAS的CO实时在线监测系统,在此平台基础上,提出了一种三角替代Voigt线型单光谱积分吸光度的快速计算方法,并与高斯-埃尔米特方法进行比较。结果表明:三角替代方法浓度反演精度仅下降0.11%,平均计算耗时缩短84.19%;三角替代Voigt线型拟合方法以极小的精度损失,大幅提高了线型拟合的运算速度。     

Cross-interference correction and simultaneous multi-gas analysis based on infrared absorption

In this paper, we present simultaneous multiple pollutant gases (CO 2 , CO, and NO) measurements by using the non-dispersive infrared (NDIR) technique. A cross-correlation correction method is proposed and used to correct the cross-interferences among the target gases. The calculation of calibration curves is based on least-square fittings with third-order polynomials, and the interference functions are approximated by linear curves. The pure absorbance of each gas is obtained by solving three simultaneous equations using the fitted interference functions. Through the interference correction, the signal created at each filter channel only depends on the absorption of the intended gas. Gas mixture samples with different concentrations of CO 2 , CO, and NO are pumped into the sample cell for analysis. The results show that the measurement error of each gas is less than 4.5%.     

An optical system for measuring nitric oxide using spectral separation techniques

An optical sensor based on differential absorption spectroscopy for real-time monitoring of industrial nitric oxide (NO) gas emission is described. The influence of gas absorption interference from sulfur dioxide (SO₂) in the environment was considered and a spectral separation technique was developed in order to eliminate this interference effect. The absorption spectrum of SO₂ around 226 nm was evaluated by the SO₂ concentration obtained using the experimentally recorded absorption spectrum around 300 nm. The absorption spectrum of NO around 226 nm was obtained by subtracting the absorption of SO₂ from the integral absorption spectrum of SO₂ and NO. The concentration measurements were performed at atmospheric pressure. The technique was found to have a lower detection limit of 0.8 ppm for NO per meter path length (SNR=2) and be immune from the influence from SO₂ on the NO measurement. The sensor based on this technique was successfully employed for in situ measurement of SO₂ and NO concentrations in the flue gas emitted from an industrial coal-fired boiler.     

超光谱大气CO_2监测仪光谱定标误差修正

超光谱大气CO_2探测需对遥感器进行精确表征及定标,其中光谱定标工作最为基础。针对传统实验室定标方法获取的波长定标系数不确定度高等特点,开展基于气体吸收法原理的光谱定标误差修正研究,该方法与仪器使用状态一致,提高了定标系数实用性。首先利用辐射传输进行了理论光谱及误差因素模拟计算,并基于大气环境模拟定标仓开展了大气XO_2吸收光谱测量实验,最后采用LM算法进行光谱误差修正迭代优化。光谱定标误差修正结果表明:光谱偏差均值由修正前的0.03 cm~(-1)下降到修正后0.008 cm~(-1),且系统性与突变性误差得以剔除,大大提高了地面光谱定标精度,为后续温室气体反演奠定了基础。     

Method of sensitivity improving in the non-dispersive infrared gas analysis system

A method of interference correction for improving the sensitivity of non-dispersive infrared (NDIR) gas analysis system is demonstrated. Based on the proposed method, the interference due to water vapor and carbon dioxide in the NDIR NO analyzer is corrected. After interference correction, the absorbance signal at the NO filter channel is only controlled by the absorption of NO, and the sensitivity of the analyzer is improved greatly. In the field experiment for pollution source emission monitoring, the concentration trend of NO monitored by NDIR analyzer is in good agreement with the differential optical absorption spectroscopy NO analyzer. Small variations of NO concentration can also be resolved, and the measuring correlation coefficient of the two analyzers is 94.28%.     

Resonant optoacoustic detector in nondispersive gas analyzer scheme

A nondispersive gas analyzer scheme is suggested, in which the resonant optoacoustic device is used for detection of air sample absorption, where modulation with the appropriate spectral filtration is carried out with the help of pure detecting gas cells. Analyzer performance for CO₂, CO, CH₄, SO₂ and NO is studied. The modulation depth for gas cells was found to be between 0.45 for NO and 0.84 for CO₂. Trace-gas detectivity is limited by acoustical noise, originating from light beam chopper at a level of 10⁻²%. Information about the influence of spectral interference on detection selectivity was obtained.     

采用离轴入射的腔增强吸收光谱研究

为了改善腔增强吸收光谱的探测灵敏度和光谱分辨率,通过将激光光束离轴注入光学谐振腔中,减小了谐振腔内振荡,提高了模式密度,使得谐振腔被近似看作为“怀特池”。采用记录波长在扫描过程中实际变化的方法,对光谱数据进行了非线性校正,省去了参考光路的布置,简化了实验光路。对二氧化碳在1．572μm处的一条弱吸收谱线进行了测量,得到了大小为1．98×10^-7cm^-1的最小探测灵敏度。实验结果表明同等实验条件下,光束离轴入射时比正轴入射时的腔增强吸收光谱具有更高的信噪比和光谱分辨率。     

Absolute, spatially resolved, in situ CO profiles in atmospheric laminar counter-flow diffusion flames using 2.3?μm TDLAS

We developed a new, spatially traversing, direct tunable diode laser absorption spectrometer (TDLAS) for quantitative, calibration-free, and spatially resolved in situ measurements of CO profiles in atmospheric, laminar, non-premixed CH₄/air model flames stabilized at a Tsuji counter-flow burner. The spectrometer employed a carefully characterized, room temperature distributed feedback diode laser to detect the R20 line of CO near 2,313?nm (4,324.4?cm^?1), which allows to minimize spectral CH₄ interference and detect CO even in very fuel-rich zones of the flame. The burner head was traversed through the 0.5?mm diameter laser beam in order to derive spatially resolved CO profiles in the only 60-mm wide CH₄/air flame. Our multiple Voigt line Levenberg?CMarquardt fitting algorithm and the use of highly efficient optical disturbance correction algorithms for treating transmission and background emission fluctuations as well as careful fringe interference suppression permitted to achieve a fractional optical resolution of up to 2.4?×?10^?4 OD (1??) in the flame (T up to 1,965?K). Highly accurate, spatially resolved, absolute gas temperature profiles, needed to compute mole fraction and correct for spectroscopic temperature dependencies, were determined with a spatial resolution of 65???m using ro-vibrational N₂-CARS (Coherent anti-Stokes Raman spectroscopy). With this setup we achieved temperature-dependent CO detection limits at the R20 line of 250?C2,000?ppmv at peak CO concentrations of up to 4?vol.%. This permitted local CO detection with signal to noise ratios of more than 77. The CO TDLAS spectrometer was then used to determine absolute, spatially resolved in situ CO concentrations in the Tsuji flame, investigate the strain dependence of the CO Profiles and favorably compare the results to a new flame-chemistry model.     

差分吸收大气CO2激光雷达的大气压力增宽修正算法

CO2作为温室气体主要成分对全球气候有重要的影响。现有的被动观测设备都只能获得单点上空的CO2浓度值,而差分吸收激光雷达在探测CO2方面具有巨大优势,可以获得较高的时空分辨率。然而,在利用差分吸收激光雷达探测CO2浓度时,其中的压力增宽有不可忽视的重要影响。基于此着重对压力增宽进行分析,提出新的修正算法,新方法同经典算法相比较,减小了反演过程中的误差。实验中分别对一例仿真信号和实测信号进行反演,最终获得了CO2浓度垂直廓线分布较为理想的结果,验证了新修正算法的可行性。